Polycarbonate lenses of the type used in eyeglasses, camera lenses, optical instruments, eyeglass shields, goggles and other protective gear, cannot be dyed at temperatures of 212.degree. F. or less, because of the high second order transition temperature (T.sub.g) (250.degree.-260.degree. F.) of the polycarbonate. Aqueous dyeing under pressure at 265.degree.-270.degree. F. for 60-90 minutes is needed to obtain good coloration. However, this long heat treatment is costly and slow, and drastically reduces the impact resistance of the polycarbonate article. During the long heat treatment, the molding-related physical arrangements undergo changes which cause the loss of impact resistance. High impact resistance is a necessary requirement for all plastic lenses, and it is a special requirement for the military.
Thus, an object of this invention is to develop a rapid solvent dyeing process with uniform dye uptake without reducing the high impact resistance or changing the haze factor of dyed polycarbonate lenses.
Polycarbonate lenses are produced by placing liquid polycarbonate monomer (undyed) and an initiator, usually an organic peroxide, e.g., isopropyl peroxide, in a mold. After polymerization is completed, the lenses are polished and cleaned. Normally, lenses are dyed by adding organic dye to the monomer and initiator blend. These dyes must be compatible with both the monomer and initiator. This process requires a significant investment for dyes and an inventory of colored lenses to provide a full range of products.
Polycarbonate articles including lenses which contain tint or dye are required for optical and nonoptical uses, such as safety glasses and sunglasses, and for industrial and military applications such as helmets with protective face shields.